Characterisation of antioxidative systems in the ectomycorrhiza-building basidiomycete Paxillus involutus (Bartsch) Fr. and its reaction to cadmium

The effect of different cadmium (Cd) concentrations (5, 50 and 500 microM) on growth, Cd accumulation and antioxidative systems was studied in Paxillus involutus, grown in liquid medium. Cd was rapidly accumulated by P. involutus and resulted in growth inhibition within 24 h. Antioxidative enzymes (superoxide dismutase (SOD), EC 1.15.1.1; catalase (CAT), EC 1.11.1.6; monodehydroascorbate radical reductase (MDAR), EC 1.6.5.4; dehydroascorbate reductase (DAR) glutathione reductase (GR), EC 1.8.1.7 and glutathione-dependent peroxidase (GPx), EC 1.11.1.9) were active in the investigated fungus. Furthermore, high concentrations of glutathione but no ascorbate were detected. Cd exposure resulted in a significant induction of SOD activity. However, activities of enzymes responsible for the detoxification of H2O2 showed no Cd-dependent increase or were only transiently induced (CAT, GPx) and no accumulation of H2O2 was detected. Exposure to low Cd concentrations (5 and 50 microM) caused an increase in GR, while 500 microM Cd led to an inhibition of GR and CAT. Increased glutathione concentrations were observed as a consequence of all Cd treatments. These results suggest that the antioxidative protection of the investigated strain of P. involutus was sufficient to avoid Cd-mediated oxidative stress. It is likely that this strain was able to detoxify high concentrations of Cd by transport of Cd into the vacuole because a high correlation between Cd and sulphur in the vacuole was detected by EDX.